This invention relates to a weight checker-sorter, which is an apparatus for weighing products intended to contain a specified number of articles to thereby determine whether each weighed product contains more or less than the specified number of the articles and to sort the weighed products accordingly.
When products to be sold are in the form of a box or a Package containing a specified number of articles, it has been known to make use of a weight checker-sorter such as described in Japanese Utility Model Publication Jikko 3-1101 to examine whether each product actually contains the specified number of the articles. As schematically shown in FIG. 6, such a weight checker-sorter may include a sorting conveyer 2 (serving as a sorter) disposed on the downstream side of a weighing conveyer 1 (serving as a weigher). A pusher 2a disposed near the sorting conveyer 2 is adapted to push each product A off the sorting conveyer 2 if it is determined not to contain a pre-selected intended number of articles a.
Having measured the weight of the product A, the weighing conveyer 1 outputs a weight signal w.sub.i indicative of the measured weight value W.sub.i to a judging means 3, as shown in FIG. 7. The judging means 3 compares the weight value W.sub.i with a standard value W.sub.b stored in a memory means 4. If the difference (W.sub.i -W.sub.b) is within an allowable limit, the weighed product A is considered to have "passed" the test. If the difference is not within the allowable limit, it is concluded that the number of the articles contained in the product A is either too large or too small, and a defect signal d is outputted from the judging means 3 to the sorting conveyer 2.
The standard value W.sub.b is initially inputted from a keyboard 5 but is thereafter updated by an updating means 10, which includes a memory means 11 and an averaging means 12. The memory means 11 serves to successively store measured weight values W.sub.i of products A which have been considered by the judging means 3 as having "passed" and the averaging means 12 serves to calculate a simple average of a plural number n of weight values W1, W2, . . . , W.sub.n and to obtain therefrom an average value W.sub.a. Thereupon, the updating means 10 outputs a standard value signal w.sub.b to cause the average value W.sub.a to be stored in the memory means 4 as the new standard value W.sub.b, thereby updating the standard weight value.
The weight of the articles a shown in FIG. 6 changes gradually during their production process due to variations in the ambient temperature and production errors. As a result, there are fluctuations in the measured weight W.sub.i of the products A. The prior art technology described above teaches how to adjust to such fluctuations by introducing a new standard weight value through an averaging process on earlier obtained weight values W.sub.i.
The weight W.sub.i of the products A, however, does not always change gradually. When articles from a new lot have been introduced or when the production process has been interrupted, for example, the weight W.sub.i of the product A may change suddenly. Consider the process shown in FIG. 8(a), for example, of filling containers 51 with a semi-liquid L from a hopper 50. The hopper 50 may be provided with a screw conveyer 52 for delivering a fixed amount of the semi-liquid L into the container 51 placed below. The hopper 50 may be provided also with a level sensor 53 such that, as soon as the top level of the semi-liquid L in the hopper 50 drops below its level, semi-liquid L from the next lot is dropped inside the hopper 50 as shown in FIG. 8(b). This causes an increase in the pressure near the bottom outlet 54, and the amount of the semi-liquid L delivered into the container 51 increases suddenly, as shown also in FIG. 8(b). As a result, both the article weight and the product weight not only change gradually but also increase suddenly, as shown by solid lines in FIGS. 3(a) and 3(b).
In such a situation, the measured product weight W.sub.i may become greater than the allowable upper limit (which is the sum of the standard W.sub.b and the weight a of a single article, or W.sub.b +a) although the product may in fact be containing the specified number of the articles. In other words, the prior art technology cannot adjust quickly enough to a situation where there is a sudden change in the article weight.